Mesta Automation. In this post you will find how to use n. Modbus with C and how to create a simulation enviroment to test your program with Modbus. Other useful resources that you can find in this post are using a Modbus simulator. Creating virtual Com ports. Using sniffer tools to debug the transmission. A Modbus TCP Client in C with another library. Getting NModbus. The C library I use the most when I need Modbus communication between pc and plcs or other components is n. Modbus. n. Modbus manages both Modbus TCP and RTU protocols, its well tested and sources are available. AllinOne Edition. PLC wiring. Develop custom IO drivers and extensions SDK. Step7 MicroWIN Upload Download Program in S7 200 PLC using USB PPI Duration 1052. Hybrid Automation Technologies 30,388 views. The new NModbus. 4 library on Git. Hub, but to compile it you need Visual Studio 2. C 6 features used. You can also download from Nu. Get by searching for NModbus. The old library on google code has bugs check comments for more informations, please consider using either the new NModbus. The old library of n. Modbus is http code. Once you extract the sources you can open the solution file, located in the src folder. Sample code. NModbus contains many samples included in the source code. Once you open it, you can go to My. Siemens S7 300 Plc Simulator' title='Siemens S7 300 Plc Simulator' />Sample project that contains many examples on how to read and write using different devices. You can check a how to video here https www. The two examples that I use the most are Modbus TCP and RTU, and an example of the code to use the library is this Modbus TCP. Tcp. Client client new Tcp. Client1. 27. 0. Modbus. Ip. Master master Modbus. Ip. Master. Create. Ipclient. read five input values. Address 1. 00. ushort num. Inputs 5. bool inputs master. Read. Inputsstart. Address, num. Inputs. Inputs i. Console. Write. LineInput 01, start. Address i, inputsi Address 1. HTB13nAnFpXXXXbHaFXXq6xXFXXXS/205782019/HTB13nAnFpXXXXbHaFXXq6xXFXXXS.jpg' alt='Siemens S7 300 Plc Simulator' title='Siemens S7 300 Plc Simulator' />Write. Multiple. Coilsstart. Address, new bool true, false, true. Serial. Port port new Serial. PortCOM1. configure serial port. Baud. Rate 9. 60. Bentley Prerequisites. Data. Bits 8. port. Siemens S7 300 Plc Simulator' title='Siemens S7 300 Plc Simulator' />Parity Parity. None. Stop. Bits Stop. Bits. One. create modbus master. IModbus. Serial. Master master Modbus. Serial. Master. Create. Rtuport. byte slave. Id 1. ushort start. Address 1. ushort num. Registers 5. read five registers. Read. Holding. Registersslave. Id, start. Address, num. Registers. for int i 0 i lt num. Registers i. Console. Write. LineRegister 01, start. Address i, registersi. Id 1. ushort start. Address 1. write three coils. Write. Multiple. Coilsslave. Id, start. Address, new bool true, false, true. Depending on the registers that you are going to read and write you have different methods, that will call different functions of the protocol, and that will return the results in 2 formats ushort or bool if you are reading multiple registers you will get array of ushorts and bools. ITDONOTWORKNModbus is supported by thousands of users, and you can find help on the NModbus google Group. Testing your program with a simulation The most common Modbus simulator is located at http www. This simulator provides both Modbus TCP and RTU protocols, and shows the content of the registers in the main windows so you can analyze the behaviour of your program directly in the tables of the simulator. Creating Virtual COM Ports to test Modbus RTU While its easy to use TCP to analyze the Modbus TCP on the host just create a socket with a 1. Modbus RTU or ASCII may require some hardware, like a null modem cable and 2 COM Ports. To avoid this you can download a null modem emulator called Com. Com open source, located at http sourceforge. Sniffer tools available for free If you need to analyze the traffic between two devices to see whats going on with your communication, there are two useful tools Wireshark is used to sniff ethernet packets and to decode the protocol. This tool can decode Modbus TCP protocol quite well and its also useful to debug the transmission. Free Serial Port Monitor is a serial port sniffer that can analyze the transmission between 2 COM Ports. Other Modbus TCP libraries While NModbus is the best choice, another Modbus TCP library is available at http www. Articles1. 62. 60Modbus TCP class. This library provides a client with some interesting features and its also useful for debugging the devices. How to video on NModbus. You can get the software configuration in the article.